Diagnosing a problem with your Isuzu oxygen sensor can require some detective work. After all, many of the same symptoms caused by a failing oxygen sensor can be seen when other components in the fuel/combustion system fail. Other problems could be a failed ignition glitch, vacuum leaks, a broken EGR valve, clogged injectors and other fuel supply issues. What kind of symptoms are you noticing? Misfires and rough idling. When you step on your gas pedal, you will feel the engine hesitate or surge. Gas mileage drops. The first step is to check the diagnostic code, but don't rely on that alone. An oxygen sensor that fails intermittently, or is just slow, might not register on the diagnostic code. Luckily, you can do other tests with simple equipment that most DIYers already have in their garages, like a digital oscilloscope. This will help measure how fast the oxygen sensor swings back and forth from the maximum to minimum levels. Check your repair manual to see what rate your Isuzu should register; that depends on what kind of fuel system is utilized. With the modern multi-port fuel injection systems, you should see a flip-flip rate of 5 to 7 times per second while the engine is running at 2,500 rpm. An oxygen sensor that is slow to respond needs to be replaced. You can install new Isuzu oxygen sensors with a set purchased from our site.